如何从csv数据拆分和填充值？

import csv

def split_and_fill(csv_file):
    # 读取csv文件
    with open(csv_file, 'r') as file:
        reader = csv.reader(file)
        data = list(reader)

    # 拆分数据
    split_data = []
    for row in data:
        split_data.append(row)

    # 填充值
    filled_data = []
    for item in split_data:
        # 根据需要的填充规则进行填充
        filled_item = item
        # 示例：如果第二列为空，则填充默认值
        if not filled_item[1]:
            filled_item[1] = 'default_value'
        filled_data.append(filled_item)

    # 保存结果
    with open('filled_data.csv', 'w', newline='') as file:
        writer = csv.writer(file)
        writer.writerows(filled_data)

# 调用函数进行拆分和填充
split_and_fill('input_data.csv')